Method of manufacturing electrical apparatus



June 20, 1961 F. J. BINGLEY METHOD OF MANUFACTURING ELECTRICAL APPARATUS Filed Nov. 1, 1955 INVENTOR.

EPA/VA Z B/A GZZ) m WUR N M R R MN MW MUJ ATTOR/Vi) United States Patent 2,989,398 METHOD OF MANUFACTURING ELECTRICAL APPARATUS Frank J. Bingley, Mead'owbrook, Pa., assignor to Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania Filed Nov. 1, 1955, Ser. No. 544,188 4 Claims. (Cl. 96-35) The present invention relates to improvements in the manufacture of picture tubes for color television receivers, and in particular to a new and improved method of manufacturing screen structures for such picture tubes.

The type of picture tube in whose manufacture my improved method is especially useful is characterized by a screen structure constituted principally of a multitude of minute phosphor elements deposited on the interior surface of the tube faceplate, different ones of these elements being responsive to electron impingement to emit light in different primary colors, e.g. red, green and blue. In the neck of the cathode ray tube there are several electron guns, one for each of the different primary colors which the screen phosphor elements are capable of emitting, and between these guns and the faceplate there is a perforated electrode whose perforations are aligned with the electron guns and with the phosphor elements in such manner that, upon application of a predetermined potential difference between the screen structure and the electrode, electrons from a particular gun impinge only upon phosphor elements emissive of a particular primary color.

It is apparent that the successful operation of a picture tube of this type depends upon the proper positioning of the electron guns and of the screen phosphor elements relative to each other and relative to the perforated electrode. Because the application of the aforementioned potential difference between the perforated electrode and the screen creates an extremely complicated field configuration within this tube, it is extremely diflicult to predict the proper positional relationships and to provide them by conventional tube manufacturing techniques.

It has previously been proposed to apply, to a cathode ray tube faceplate, a calibration grid which is shaped to conform to the structural peculiarities of the faceplate and also to the distortions in beam scanning pattern caused by the peculiarities of the beam deflection system. To this end the beam of the tube was caused to scan a pattern corresponding to the desired calibration grid on the internal phosphor screen of the tube, the resultant pattern of illuminated screen areas was photographed from the 1 to produce calibration marks on the faceplate of the same tube which was used to determine their locations with suflicient accuracy, there are several reasons why a similar method would be entirely unsatisfactory for determining the locations of the color phosphor elements in color television picture tubes of the type under consideration. In

particular the light refraction which occurs within the tube faceplate would introduce a degree of optical distortion into the exteriorly formed photographic image and into the projected pattern reproduced thereby, which is much greater than can be tolerated in the locations of the phosphor elements of a practical color picture tube. Furthermore the degree of such refraction varies from one faceplate to another so that a photo-graph of the beam impingement pattern produced in one tube could not be used to determine the locations of the phosphor elements M the interior side, of the faceplate.

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in another tube. Finally, the presence of the perforate electrode, within a color television tube of the type under consideration, imparts to the paths which the electrons follow on their way to the faceplate degrees of distortion which vary for different areas of the faceplate. I have found that these variations cannot be reproduced by photography and projection from the exterior side of the faceplate, when it is desired to make a number of screen structures from a single photograph, owing to inevitable variations in the shapes of different faceplates.

Accordingly it is a primary object of my invention to provide a new and improved method of manufacturing picture tubes for color television receivers.

It is another object of my invention to provide a new and improved method of manufacturing a screen structure for the type of color television picture tube which has been described.

It is still another object of my invention to provide a method of manufacturing screen structures for incorporation in color television picture tubes of the type which has been described, this method being particularly adaptable to use in mass production.

To the foregoing ends I provide, initially, a cathode ray tube envelope containing a faceplate, electron guns and 'a perforated electrode similar to those of a picture tube, these components being disposed so that they occupy positions which are substantially identical to the positions which the corresponding components should occupy within a picture tube. In addition I equip this envelope with focusing, accelerating and deflecting apparatus which is substantially identical to that which is to be used in and with a picture tube. Unlike a picture tube, however, the faceplate of the aforementioned envelope is internally coated with a material which is responsive to electron In a preferred case this coating has substantially lower light transmissivity than the faceplate and is responsive to electron impingement to become substantially insoluble in water. The apparatus contained within the envelope in question is then caused to operate in a manner which simulates that of a picture tube, except that only one of the three electron guns is energized at any given time. This energized gun projects electrons upon the material coating the interior side of the'faceplate in a pattern which corresponds to the pattern of electron impingement from the corresponding gun in an actual picture tube, thereby altering the aforementioned characteristics of the coating, as for example by rendering it insoluble. The faceplate which has been treated in this manner is then utilized to form an optical mask whose light transmissivity varies in accordance with the electron-produced variations in the coating characteristics as viewed from the interior side of the faceplate. To this end the unimpinged portions of coating material are washed off the faceplate while the impinged portions are left in place and a photographic image is made of the pattern of remaining portions from This image constitutes the aforementioned optical mask which is then used in a photographic process of depositing phosphor materials in a pattern corresponding to the variations in light trans missivity of the mask on any number of other faceplates, this process involving the exposure of each of said faceplates to illumination through the mask from its interior side. -The aforedescribed exposure to electron impingement, washing and image formation is repeated, using fresh electron-sensitive coatings, with the different guns in turn, each of the optical masks thus formed being suitable for use in the deposition of difierent color phosphor elements on actual picture tube faceplates.

The details of specific steps which may be taken to achieve the aforedescribed results are explained herein- 7 Patented JuneZO, 1961 after with reference tothe'accompanying drawings where- FIGURE 1 shows, in schematic form, apparatus for forming areas of distinctive light transmissivity in positions corresponding to those in which it is desired to form phosphor elements emissive of light of a particular color in an actual color television picture tube;

FIGURE 2 shows, again in schematic form, apparatus which may be used to form a photographic image of the portions of different light transmissivity formed by the apparatus of FIGURE 1; and

FIGURE 3 shows, also in schematic form, apparatus for utilizing the photographic image formed by the apparatus of FIGURE 2 to form the phosphor elements of an actual screen structure.

FIGURE 1, to which reference may now be had, represents a so-called demountable cathode ray tube, that is one whose envelope is conveniently separable into two separate portions 11 and 12, the portion 11 being constituted of the neck portion of the tube and the fian'ng,

conical portion which connects the neck to the faceplate, While the portion 12 is principally constituted of the faceplate 12a and a flange extending back from the faceplate toward the flaring portion of the envelope. The two separate portions 11 and 12 of the envelope 10 are joined at abutting flanges designated 13 in FIGURE 1, which may be secured together in any convenient manner, e.g. by bolts 14. A sealing material is preferably placed between the abutting flanges 13 so as to make an airtight joint between these flanges. Finally an orifice 15 is pro vided in the wall of envelope portion 11, this orifice being suitable for connection to a vacuum pump by means of which the interior of the envelope 10 may be evacuated.

Within the envelope 10 are disposed all of the components which would be included in a picture tube of the type under consideration with the exception of the screen structure. Moreover these components are disposed within envelope 10 in the same spatial relationships which they would occupy in such a tube. Thus there are disposed within envelope 10 three separate electron guns 16, 17 and 18. There is also provided a grid of parallel wires which extend in a direction normal to the plane of the paper in FIGURE 1 and which are schematically represented therein by circles 19. It will be understood that in an actual embodiment there may be many more grid wires than have been illustrated in FIGURE 1, the number illustrated having been reduced for greater clarity. These wires are mounted on a suitable frame member 20 which, in turn, is supported on bosses 21 which are preferably constituted by protrusions from the inner surface of the envelope 10. This envelope is further equipped with the usual internal electrode coatings and appropriate external contacts thereto (not shown) and with a conventional deflection yoke 22. All of the foregoing components may take any one of a number of conventional forms and therefore need not be described in greater detail here.

As has been pointed out previously, the envelope 10 does not contain a conventional screen structure. Instead there is deposited on the interior surface of its faceplate 12a a layer 23 of a material which has the property of being soluble in water prior to impingement by electrons and of becoming insoluble in water in consequence of such an electron impingement. Preferably the material in question also has substantially lower light transmissivity than the glass faceplate of the tube. A number of materials suitable for use in this manner are known. They include, for example, manganese activated polyvinyl alcohol mixed with an appropriate opaque dye. To permit the establishment, between the wire grid 19 and the electron sensitive layer .23, of the same potential difference which will be established in an actual picture tube between the wire grid and the screen structure, the layer 23 is either coated on its interior surface with a layer (not shown) of conductive material, such as aluminum, of

4 electron permeable thickness, or alternatively a conductive material is incorporated directly into layer 23. In either case suitable electrical connections (not shown) are made to this conductive material and to the wire grid 19, and a potential difference corresponding to that which it is intended to use in an actual picture tube is established between'the grid and thelayer 23. The tube is now evacuated and one of the three electron guns, e.g. gun 16, is energized .so, as to project an electron beam similar to that which would be projected in an actual picture tube from the corresponding gun toward the faceplate of the envelope v10. This beam is deflected by the de flection yoke 22 so as to trace on layer 23 a conventional scanning raster modified only by the electron lens effect of the potential difference between the grid wires 19 and the layer 23. As a result of this operation the layer 23 will be impinged by electrons in precisely the same areas in which the screen structure of an actual picture tube would be impinged by electrons from the corresponding electron gun, and the portions of the material constituting layer,23which occupy these same areas will respond to such impingement by becoming insoluble. The portions which have thus been rendered insoluble are represented in FIGURE 11 by the blacked out portions of layer 23, although it will be understood that no actual change in the .light .transmissivity of these portions takes place.

At this point the electron emission from the gun is interrupted and the tube is disassembled into its two separateenvelope components. The wire grid 19, together with its frame 20, is removed from the envelope portion 12 and this envelope portion is then washed with water so as to removefrom its faceplate all but those portions of the material .23 which have been subjected to impingement by electronsand which have therefore been rendered insoluble, i.e. those .portions which are blacked out in FIGURE 1. The resultant appearance of envelope portion 12 is, schematically illustrated in FIGURE 2 to which more particular reference may now be had. This envelope portion .12 includes the faceplate 12a which now has deposited, on its interior surface, spaced portions 24 constitutedby theflbeam impinged portions of the electron sensitive layer23 in FIGURE 1. This faceplate 12a is subjected to diffuse illumination from its exterior side. This illumination may be produced, for example, by a group of fluorescent lamps 25 illuminating the faceplate through a diffusing screen 26. On the interior side of the faceplate, and preferably in axial alignment therewith, is disposed an unexposed photographic plate 27 upon which an image of the elements 24, produced by the diffuse illumination, is projected by way of an appropriate projection lens system 28. As a result of this projection the photosensitive plate 27 is exposed in spaced portions whoselocations correspond to the locations of the portions of faceplatelZa which are not occupied by elements 24. The latent image thus formed in photosensitive plate 27 is then developed and the resultant transparency 29, which is shown in FIGURE 3, is utilized in the manufacture of an actual cathode ray tube screen structure.

The transparency 29, which may be characterized as a .negative transparency, has opaque portions (represented by blacked out areas in FIGURE 3) in positions which correspond to those of the illuminated portions of the photosensitive plate 27. This transparency 29 is disposed on the interior side of a faceplate 30 which is to be used eventually as the faceplate of an actual color television picture tube in the same spatial relation as existed between the faceplate 12a and the photosensitive plate 27 during exposure of the latter. The interior surface of this faceplate is coated with a layer 31 of a material-which is responsive to illumination to become insoluble in water and this material is subjected to illumination from a light source 32 through a condensing lens system 33, through the transparency 29 and through another lens system 34 which may be similar to lens system 28 of FIGURE 2. As a result of this illumina- FIGURE 1.

posited on these soluble portions. there remain in place those portions of the material which aesasss tion' the material of the layer 31 is rendered insoluble in spaced portions whose locations correspond to the locations of the transparent portions of transparency 29 and which therefore also correspond to the locations of the electron impinged portions of the electron sensitive layer 23 of FIGURE 1. The portions of layer 31 which are thus rendered insoluble are indicated in solid black in FIGURE 3, although it will be understood that no change 'moved those portions of layer 31 which have not been subjected to illumination and which have therefore remained soluble, together with the phosphor material de- On the other hand have been exposed to illumination and which have thereby been rendered insoluble, together with the phosphor material deposited on these latter portions. As a result there is produced, on the interior surface of faceplate 30, a pattern of spaced phosphor elements which corresponds precisely to the pattern of electron impinged portions of electron sensitive layer 23 of FIGURE 1.

These phosphor portions are thus located precisely in the positions they should occupy in the completed tube for impingement by the electron beam which emanates from a gun located in a position corresponding to that of gun 16 in the apparatus of FIGURE 1. The aforedescribed technique of utilizing a negative transparency to form the phosphor strips is more fully described in the copending application of Paul D. Payne, Jr., Serial No.

376,345, filed August 25, 1953, Patent No. 2,950,193 and assigned to the assignee of the present invention. As pointed out in that application the light sensitive material for use as layer 31 may be a stock solution of photosensitive gel consisting, for example, of 25 grams of polyvinyl alcohol and 600 cc. of distilled water. Various polyvinyl alcohols of different average viscosity, and hence of different degrees of polymerization may be used. However it has been found that satisfactory results are obtained with a polyvinyl alcohol of medium viscosity such as prepared by DuPont under the trade name Elvanol 5222. This alcohol is added to the distilled water, dissolved therein and filtered, after which 200 cc. of ethyl alcohol and 25 cc. of a solution of ammonium or potassium dichromate containing 22 grams of the salt for each 100 cc. of water are added.

In the successful operation of the apparatus of FIG- URES 2 and 3, the location of the lens systems 28 and 34 is important. More particularly I have found that the nodal point of each of these lens systems should be located at a point which corresponds substantially to the location of the effective electron center within the cathode ray tube into which the screen structure constructed in accordance with my invention will eventually be incorporated. By effective electron center I mean the point of intersection of straight lines drawn, for each of the paths which electrons may follow within the completed tube, so as to pass through the points of intersection of this path with the plane of the perforated electrode and with the screen structure. I have found that the location of the lens nodal points in this manner gives rise to an accurate reproduction of the areas of electron impingement in FIGURE 1, whereas failure to locate the lens in this manner introduces serious inaccuracies. Clearly this lens location requirement can be met only if the mask is formed by photographing the faceplate from its interior side and only if the phosphor strips are formed by exposure of the faceplate from its interior side.

To deposit phosphors of the other two colors on the same faceplate '30 it is first necessary to manufacture two additional negative transparencies. To this end the apparatus of FIGURE 1 is utilized again, first by operating only electron gun 17 and then by operating only electron gun 18 so as to expose two new electron sensitive layers deposited on the interior surface of faceplate 12a. Each of the additional beam exposed layers thus produced is utilized in an apparatus like that of FIGURE 2 to produce corresponding exposed photosensitive plates. These photosensitive plates, in turn, are utilized to produce negative transparencies which are then used in the apparatus of FIGURE 3 to produce selective exposure of light sensitive material on faceplate 30 in those spaced portions in which it is desired to deposit phosphors emissive of light of the other two colors.

Once phosphors of all three colors have been deposited in their appropriate locations upon faceplate 30, the remaining conventional assembly operations for a complete picture tube are carried out. Since these remaining operations are well known they need not be mentioned I here.

It will be understood that considerable latitude is available to the practitioner of my invention in the choice of specific auxiliary alignment apparatus which must be vused at each stage of the process in order to maintain the desired spatial relationships between the various apparatus components. However, since this alignment apparatus may take any one of a number of conventional forms, no specific illustration and description thereof is believed to be required.

- It will also be understood that my invention may be .used to form components of the screenstructure other than the phosphor elements. For example, in a picture tube of the type under consideration it is sometimes desirable to deposit narrow strips of opaque material in the spaces between adjoining phosphor strips so as to minimize the degree to which light of one color emitted from any one phosphor strip in contaminated by light of different colors emitted from adjoining phosphor strips. To deposit such strips of opaque material all three guns of thedemountable tube of FIGURE 1 are operated simultaneously and the resultant electron-sensitized layer is used to form a corresponding transparency which is,

in turn, used to form the opaque strips by the photographic technique described.

The deposition ofsuchopaque strips prior to the deposition of color phosphor strips in accordance with my invention also tends to minimize the effects of errors in color phosphor strip positioning which may result from the many manipulations involved in the manufacture and utilization of the several different transparencies used for the deposition of the color phosphors. This improvement stems from the fact that portions of the phosphor strips which are slightly misaligned are then hidden behind opaque strips and have no effect upon the visible light emitted from the screen structure. Since the locations of all of the opaque strips are determined simultaneously (by simultaneous operation of all three electron beams), their relative positions tend to be reproduced more accurately than the relative positions of differently colored phosphor strips (whose locations are not all determined simultaneously) The aforedescribed improvement in accuracy of phosphor strip positioning may also be obtained, even when no opaque strips are actually deposited on the faceplate, by depositing each set of difierent color phosphor strips by a photographic method of the kind described but using, for each exposure of the photosensitive material coating the faceplate, a transparency which has both the variations in opacity necessary for the formation of the opaque lines and the variations in opacity suitable for depositing a particular color phosphor.

While the invention has been described in relation to a tube using a perforated electrode in the form of a parallel wire grid, it will be understood that it is also applicable to any other perforated electrode configuration. It is therefore apparent that a number ofspecific modifications of the process described hereinbeforermay-ybe, made .Without departing from the scope ofmy ,inventiveconcept, and I desire the latter to be limited only by the, appended claims.

.I claim:

1. In the process of constructing a'cathode ray tube, the steps of: scanning with an electronbeam tho e area of a coating on the concave interior surface of an evacuatedenvelope which are susceptible of being impinged by said beam through a perforatedelectrode locatednear said surface and maintained at a more,negative potential than said surface, said coating being optically distinguishable from said surface and having. substantially different solubility before and after electron impingement;

dissolving those portions of saidcoatinghaving the greater of said different solubilitiesthereby to develop a visible record of said beam impingement; photographing ,said record through a lens system having ,a nodal point'vlocated in substantially the same position relative to said coating as the effective electron centerof said scanning beam; developing said photograph into a visible image of said record; and projecting saidimage. onto a photosensitive material coating the interior surface of acathode ray tube faceplate having substantially the same interior configuration as said scanned surface through a lens system having substantially the same optical characteristics as said photographing lens systemandjhaving its nodal point located in substantially the sameposition relative to said faceplate surface in which said etfectiveelectron center is located relative to said scanned surface, said photosensitive materialhaving reduced solubility after projection.

2. The process of claim 1 further characterized in that said coating is a soluble material deposited on the concave side of a substantial replica of said faceplate, said material having substantially lower light transmissivity than said replica and being responsive to electron impingement to become substantially insoluble.

3. The process of claim Zcharacterizedinthat said photographing of said visible record of beam impingement involves illuminating said replica with diflused light from the side opposite that having said coating.

4. In the process of constructing a cathode ray' tube, the steps of: scanning with an electron beam those areas saidsurface and maintained ate more negative potential than said surface, said coating being optically distinguishable 'from said surface and ,having substantially difierent solubility before and after electron impingement; dissolving those portions of said coating having the greater of said diiferent solubilities thereby to develop a visible record of said beam impingement; photographingsaid record through a lens system having a nodal point located in substantially the same position relative to said coating as the effective electron center of said scanning beam; developing said photograph into a visible image of said record; projecting said image onto a photosensitive material coating the interior surface of a cathode ray tube faceplate having substantially the sameinterior configuration as said scanned surface through alens system having substantially the same optical characteristics as said photographing lens system and having its nodal point located in substantially the same position relative tonsaid faceplate surface in which said effective electron center is located relative to said scanned surface, said photosensitive material being soluble prior to illumination and becoming insoluble in consequence to illumination; coating all areas of said photosensitivematerial with a phosphor; and dissolving portions of said photosensitive coating which have remained soluble after said image projection, thereby removing phosphor deposited on said portions while leaving in place phosphor deposited on portions which have become insoluble through illumination.

References Citedin thefile ofthis patent UNITED STATES PATENTS OTHER REFERENCES Comptes Rendus, vol. 235, p. 503 (1952). 

4. IN THE PROCESS OF CONSTRUCTING A CATHODE RAY TUBE, THE STEPS OF: SCANNING WITH AN ELECTRON BEAM THOSE AREAS OF A COATING ON THE CONCAVE INTERIOR SURFACE OF AN EVACUATED ENVELOPE WHICH ARE SUSCEPTIBLE OF BEING IMPINGED BY SAID BEAM THROUGH A PERFORATED ELECTRODE LOCATED NEAR SAID SURFACE AND MAINTAINED AT A MORE NEGATIVE POTENTIAL THAN SAID SURFACE, SAID COATING BEING OPTICALLY DISTINGUISHABLE FROM SAID SURFACE AND HAVING SUBSTANTIALLY DIFFERENT SOLUBILITY BEFORE AND AFTER ELECTRON IMPINGEMENT, DISSOLVING THOSE PORTIONS OF SAID COATING HAVING THE GREATER OF SAID DIFFERENT SOLUBILITIES THEREBY TO DEVELOP A VISIBLE RECORD OF SAID BEAM IMPINGEMENT, PHOTOGRAPHING SAID RECORD THROUGH A LENS SYSTEM HAVING A NODAL POINT LOCATED IN SUBSTANTIALLY THE SAME POSITION RELATIVE TO SAID COATING AS THE EFFECTIVE ELECTRON CENTER OF SAID SCANNING BEAM, DEVELOPING SAID PHOTOGRAPH INTO A VISIBLE IMAGE OF SAID RECORD, PROJECTING SAID IMAGE ONTO A PHOTOSENSITIVE MATERIAL COATING THE INTERIOR SURFACE OF A CATHODE RAY TUBE FACEPLATE HAVING SUBSTANTIALLY THE SAME INTERIOR CONFIGURATION AS SAID SCANNED SURFACE THROUGH A LENS SYSTEM HAVING SUBSTANTIALLY THE SAME OPTICAL CHARACTERISTICS AS SAID PHOTOGRAPHING LENS SYSTEM AND HAVING ITS NODAL POINT LOCATED IN SUBSTANTIALLY THE SAME POSITION RELATIVE TO SAID FACEPLATE SURFACE IN WHICH SAID EFFECTIVE ELECTRON CENTER IS LOCATED RELATIVE TO SAID SCANNED SURFACE, SAID PHOTOSENSITIVE MATERIAL BEING SOLUBLE PRIOR TO ILLUMINATION AND BECOMING INSOLUBLE IN CONSEQUENCE TO ILLUMINATION, COATING ALL AREAS OF SAID PHOTOSENSITIVE MATERIAL WITH A PHOSPHOR, AND DISSOLVING PORTIONS OF SAID PHOTOSENSITIVE COATING WHICH HAVE REMAINED SOLUBLE AFTER SAID IMAGE PROJECTION, THEREBY REMOVING PHOSPHOR DEPOSITED ON SAID PORTIONS WHILE LEAVING IN PLACE PHOSPHOR DEPOSITED ON PORTIONS WHICH HAVE BECOME INSOLUBLE THROUGH ILLUMINATION. 